Hmm, what kind of server are you getting the files from, HTTP or FTP?

If it's FTP, you can issue a command to request a dir; for HTTP, I think what you'd have to do is issue a request for the file if it's newer than the one you have.

I'm pretty sure there's a header for that, but I can't remember offhand what it might be. Sorry!

But look into HTTP headers on google or w3c.org, and you're likely to find what you're looking for.
--
Mike